1. Field of the Invention
This invention relates to magnetic recording, and in particular to electromagnetic drive circuitry for anhysteretic duplication of a pre-recorded floppy diskette.
2. Description Relative to the Prior Art
Magnetic recording media play a critically important role in the storage of digital data. A floppy diskette or disk is currently one of the most commonly used magnetic media; millions of both pre-recorded and unrecorded diskettes are sold for use in personal, office and workstation computer systems.
A diskette must be appropriately formatted before it can be utilized in a computer system. Formatting involves recording markers on the diskette which divide the recording surface into identified sectors, and which provide synchronizing signals essential in recording and reading information on the diskette. High-track-density applications of formatting may also include writing tracking servo signals over the recording surface. Formatting can be a very time consuming job, and an unformatted diskette is usually formatted on a diskette drive of the user's system by recording formatting signals under control of the disk operating system (DOS) of the computer. Pre-formatted diskettes are available in the marketplace, and in the prior art such diskettes have generally also been formatted in so-called real time by the manufacturer on standard disk drives. Using the DOS of an associated computer, these diskettes are individually formatted by means of signals applied to the recording head of the disk drive in substantially the identical manner to the process used in a personal computer diskette formatting operation.
There is also an extremely large market for pre-recorded diskettes containing application programs. Word processing programs, database programs, computational programs, and games programs are just a few of the myriad pre-recorded programs available on diskettes. Generally, these programs have similarly been transferred from master recordings to slave diskettes by conventional re-writing. The master is read by a standard disk drive, and the read signals are fed in real time to one or more satellite recording drives on which the slave diskettes are mounted. This method of duplication, which is essentially the same as the pre-formatting method described above, is similarly slow, laborious, and expensive to implement.
It is also known in the art that a magnetic pattern may be anhysteretically transferred from a master medium to a slave medium by means of a magnetic transfer field applied to the master and slave. In anhysteretic processing, the master medium, which typically has a coercivity of about three times that of the slave medium, is placed in intimate contact with the slave medium. The in-contact master and slave are both subjected to a decreasing-amplitude alternating-polarity magnetic field. The transfer field is not of great enough strength to substantially affect the magnetization of the master; the transfer field does, however, successively switch the magnetization of the magnetic particles of the slave between two magnetic states. As the amplitude of the transfer field is decreased, the remanent magnetization of the slave assumes a final value proportional to the magnetization of the master.
Kokai No. 63-183623 discloses apparatus for pre-formatting a flexible slave disk by an anhysteretic transfer process. For that purpose, the flexible disk is mounted on a rotatable shaft between opposing poles of a pair of electromagnets which cooperatively provide a magnetic transfer field. In order to subject opposite surfaces to a transfer field of similar intensity, the flexible disk is held in a fixed plane midway between opposing poles of the two electromagnets. This is accomplished by sandwiching the slave disk between a pair of rigid or hard disks, which also serve as pre-formatted master media.
Although pre-formatted information is duplicated on a flexible disk by an anhysteretic transfer process, the drive circuitry of 63-183623 introduces additional cost and complexity into the duplication process. This is because the two electromagnetics and their associated drive coils must have matched magnetic characteristics in order to subject opposing surfaces of the flexible slave disk to a magnetic transfer field of substantially the same intensity.